Designer Matter: Meta-Material Interactions with Light and Sound

Dear Faculty and Students,

The Physics Department and Center for Theoretical Physics will conduct a seminar Thursday May 16 at 12:00 pm in Namm Room 823.  Faculty and students are welcome. Light refreshments will be served.

Topic:

Metamaterials are artificial materials with properties well beyond what offered by nature, providing unprecedented opportunities to tailor and enhance the interaction between waves with materials. In this talk, I discuss our recent research activity in electromagnetics, nano-optics and acoustics, showing how suitably tailored meta-atoms and arrangements of them open exciting venues to manipulate and control waves in unprecedented ways. I will discuss our recent theoretical and experimental results, including metamaterials for scattering suppression, metasurfaces to control wave propagation and radiation, large nonreciprocity without magnetic bias, giant nonlinearities in properly tailored metamaterials and metasurfaces, and active metamaterials. Physical insights into these exotic phenomena, new devices based on these concepts, and their impact on technology will be discussed during the talk.

Presented by:

Prof. Andrea Alù

Physics Seminar: Control of light-matter interaction in 2D materials

Presented by:
Prof. Vinod Menon
of
City College of CUNY
New York, NY

Two-dimensional (2D) Van der Waals materials have emerged as a very attractive class of optoelectronic material due to the unprecedented strength in its interaction with light. In this talk I will discuss approaches to enhance and control this interaction by integrating these 2D materials with microcavities, and metamaterials. I will first discuss the formation of strongly coupled half-light half-matter quasiparticles (microcavity polaritons) [1] and their spin-optic control [2] in the 2D transition metal dichacogenide (TMD) systems. Prospects of realizing condensation and few photon nonlinear switches using Rydberg states in TMDs will also be discussed. Following this, I will discuss the routing of valley excitons in 2D TMDs using chiral metasurfaces [3]. Finally, I will talk about room temperature single photon emission from hexagonal boron nitride [4] and the prospects of developing deterministic quantum emitters using them [5].

References

[1] X. Liu, et al., Nature Photonics 9, 30 (2015)

[2] Z. Sun et al., Nature Photonics 11, 491 (2017)

[3] S. Guddala et al., ArXiv 1811.00071

[4] Z. Shotan, et al., ACS Photonics 3, 2490 (2016)

[5] N. Proscia, et al. Optica 5, 1128 (2018).

 

 

         Light refreshments will be served.

Physics Seminar

Title: Quantum Many-Body Physics of Qubits

Professor Leonid Glazman

Yale University,

New Haven, CT, USA

Abstract:

The ongoing development of superconducting qubits has brought some basic questions of many-body physics to the research forefront, and in some cases helped solving them. I will address two effects in quantum condensed matter highlighted by the development of a fluxonium qubit. The first one is the so-called cosine-phi problem stemming from the seminal paper of Brian Josephson: the predicted there phase dependence of the dissipative current across a Josephson junction was observed in a fluxonium, after nearly 50 years of unsuccessful attempts by other techniques. The second one is the dynamics of a weakly-pinned charge density wave: we predict that the dynamics may be revealed in measurements of microwave reflection off a superinductor, which is a key element of the fluxonium.

Physics Seminar

The Physics Department and Center for Theoretical Physics will be having a seminar Thursday, October 18 at 12:00 pm in Namm Room 823.  Faculty and students are welcome.

Title

Superconducting proximity effect in two-dimensional semiconductor-superconductor structures

Abstract

Progress in the emergent field of topological superconductivity relies on the synthesis of new material combining superconductivity, low density, and spin-orbit coupling (SOC). Theory indicates that the interface between a one-dimensional semiconductor with strong SOC and a superconductor hosts Majorana-modes with nontrivial topological properties. We discuss the recent developments in the epitaxial growth of Al on InAs nanowires was shown to yield a high-quality superconductor-semiconductor system with uniformly transparent interfaces and a hard induced gap, indicted by strongly suppressed subgap tunneling conductance. We have developed a two-dimensional (2D) surface InAs quantum wells with epitaxial superconducting Aluminum, yielding a planar system with structural and transport characteristics as good as the epitaxial nanowires. The realization of 2D epitaxial superconductor-semiconductor systems represents a significant advance over wires, allowing extended networks via top-down processing. We present our recent developments in materials synthesis and growth of these density-controlled surface 2D electron-gases and demonstrate Josephson junctions with highly transparent contacts. These developments have to lead to unprecedented control over proximity effect in semiconductors where electron densities can be tuned using a gate voltage. We discuss potential applications of this new material system that can serve as a platform for low power circuits, gate-based qubits as well as exploring topological superconductivity for computation.

 

Physics Seminar: Bragg reflector-induced increased self-absorption of emitted photons in optically-thin GaAs/AlGaAs double heterostructures

The Physics Department and Center for Theoretical Physics will be having a seminar Thursday, October 26 at 12:00 pm in Namm Room 823.  Faculty and students are welcome. Light refreshments will be served.

Dr. Patrick Folkes
Army Research Laboratory
Adelphi, MD, USA

Abstract:
Time-resolved photoluminescence measurements on a set of molecular beam epitaxy (MBE)-grown GaAs/AlGaAs double heterostructures (DHs) are used to determine that a distributed Bragg reflector between the substrate and the DH significantly increases the self-absorption of emitted photons in optically-thin DHs whose thickness is comparable to or less than the wavelength of the emitted light at the GaAs bandedge. The Bragg reflector-induced increased self-absorption of emitted photons in optically thin DHs can be attributed to multiple reflections of emitted photons from the Bragg reflector and the air/semiconductor interface.

Physics Seminar: Charged Lepton Flavor Violation at Fermilab: The Mu2e Experiment

Presented by:
Dr. Kevin Lynch,
York College of CUNY
Jamaica, NY

Abstract:
The Mu2e Experiment at Fermilab will search for the coherent, neutrinoless conversion of a muon to an electron in the field of an atomic nucleus. Such charged lepton flavor violating events have never been observed, but are predicted to occur in many Beyond the Standard Model scenarios at rates accessible to our experiment. I outline the physics and key issues for the experiment, other CLFV signatures accessible to our apparatus, our progress on design and construction to date, and prospects for the future.

Faculty and students are welcome.

Physics Seminar: Quantum materials: insights from near field nano-optics

Presented by
Prof. Dmitri Basov
Columbia University
New York, NY, USA

Abstract
In 1944 Hans Bethe reported on “the diffraction of electromagnetic radiation by a hole small compared with the wave-length” [Physical Review 66, 163 (1944)]. This seminal paper was among the early precursors to a new and vibrant area of research: near field nano-optics. I will discuss recent nano-optical experiments on quantum materials including: transition metal oxides undergoing the insulator to metal transition and graphene. Central to the nano-optical exploration of quantum materials is the notion of polaritons: hybrid light matter modes that are omnipresent in polarizable media. Infrared nano-optics allows one to directly image polaritonic standing waves [Science 343, 1125 (2014), Nature Materials 14, 1217 (2015)] yielding rich insights into the electronic phenomena of the host material supporting polaritons [Science 354, 195 (2016)]. I will give a progress report on the search for the role of the Berry phase in the properties of graphene via transient polaritonic imaging [Nature Photonics 10, 244 (2016)]. In a parallel development, we harnessed near field optics to uncover the elusive electronic and magnetic phases that occur only at the nano-scale in the vicinity of the insulator to metal transition in correlated oxides [Nature Physics 13, 80 (2017) and Nature Materials 15, 956 (2016)].

Physics Seminar: Spin transport by a supercurrent in a room-temperature magnon Bose-Einstein condensate

Speaker: Dr. Oleksandr Serha
University of Kaiserslautern
Kaiserslautern, Rhineland-Palatinate, Germany

Abstract:
With the fast growth in the volume of information being processed, researchers are charged with the task of finding new ways for fast and energy efficient computing. An extraordinary challenge is the use of macroscopic quantum phenomena such as magnon Bose-Einstein condensates (BEC) for the information transfer and processing.

Here, I present experimental evidence for the excitation of a supercurrent—the transport of angular momentum driven by a phase gradient in the wave function of a magnon BEC. In our experiments, the magnon BEC was formed at room temperature by a para­met­rically populated magnon gas in a single-crystal ferrimagnetic film of yttrium iron garnet (Y3Fe5O12, YIG). The temporal evolutions of the magnon density was studied by wave­vector-, frequen­cy-, time- and space-resolved Brillouin light scattering spectros­copy. It has been found that local heating of the YIG film by focused laser light creates a spatially varying phase shift imprinted into the BEC wavefunction and, thus, propels the outflow of condensed magnons from the heated area. This outflow does not alter the dynamics of a non-coherent gaseous magnon phase but decreases the density of the freely evolving magnon BEC in the heated area. Moreover, it creates a solitary magnon wave, which pro­pa­gates many hundreds of BEC’s wavelengths through the “cold” magnon condensate.

Physics Seminar: Transient superconductivity from electronic squeezing of optically pumped phonons

Presented by

Prof. David Reichman of Columbia University

Abstract:
Advances in light sources and time-resolved spectroscopy have made it possible to excite specific atomic vibrations in solids and to observe the resulting changes in electronic properties, but the mechanism by which phonon excitation causes qualitative changes in electronic properties has remained unclear. Here we show that the dominant symmetry-allowed coupling between electron density and dipole active modes implies an electron-density-dependent squeezing of the phonon state that provides an attractive contribution to the electron–electron interaction, independent of the sign of the bare electron–phonon coupling and with a magnitude proportional to the degree of laser-induced phonon excitation. Reasonable excitation amplitudes lead to non-negligible attractive interactions that may cause significant transient changes in electronic properties, including superconductivity. The mechanism is generically applicable to a wide range of systems, offering a promising route to manipulating and controlling electronic phase behavior in novel materials.

Physics Seminar presents
Gravitational Wave Observations and the Physics of Neutron Stars

Guest Speaker: Simone Dall’Osso of SUNY Stony Brook

The first direct detection of gravitational waves (GW) from a binary black hole made by Advanced LIGO has opened the era of GW astronomy. Sources for the current detectors are catastrophic events involving neutron stars (NS) and black holes (BH), isolated or in binaries, in which huge amounts of energy are released in very small regions and short timescales. Besides GWs, bright electromagnetic (EM) transients, as well as copious emission of neutrinos and ultrarelativistic cosmic rays are expected in association to such events, making them ideal targets for multi-messenger observations. Because GW interact so weakly with the environment, they are unique probes of the physical processes occurring in the extremely dense and turbulent regions where NS/BHs form and/or collide. Because photons are easily emitted (and detected) from the surrounding regions, on the other hand, EM transients are the counterparts to GW sources that we can more effectively reveal and study. I will focus in particular on a class of highly magnetized, millisecond spinning NS, that could form both in the core-collapse of massive stars and in binary NS mergers. Such NS have been proposed as possible sources of the brightest EM transients (gamma-ray bursts, super-luminous supernovae), and as progenitors of a galactic population of peculiar X-ray pulsars (magnetars). I will present a mechanism, the so-called “spinfip” instability, by which newly born, highly magnetized, millisecond spinning NS can also produce powerful and distinctive GW signals carrying pristine information about the physics of their interiors and the equation of state (EOS) of matter at supra-nuclear density. The EM emission expected in association with these GW signals is particularly bright and carries its own signatures of the millisecond spinning NS: this makes these sources ideally suited for multimessenger studies.